This invention relates to transceiver circuitry. More particularly, this invention relates to voltage-controlled oscillators for use with transceiver circuitry.
Periodic clock signals are often used to facilitate the operation of transceiver circuitry (e.g., for data synchronization or modulation). Phase-locked loop (“PLL”) circuitry is often used to generate such a periodic clock signal, which can often be substantially synchronized in frequency and phase to a reference clock signal. One key component of PLL circuitry is voltage-controlled oscillator (“VCO”) circuitry, which can generate a clock signal whose phase and frequency vary according to a voltage of an input control signal.
Many challenges exist in the design of effective VCO circuitry. For instance, it is desirable to achieve a relatively high bandwidth, so that the frequency of the output clock signal generated by the VCO circuitry can vary over a relatively wide range. A relatively high bandwidth can be especially important if the VCO circuitry is used in a programmable logic device (“PLD”), because the VCO circuitry must be able to support a relatively large number of communication protocols. As another example, it is desirable to keep the phase noise of the clock signal relatively low. (Phase noise is a metric commonly used to quantify the jitter of a clock signal.) Traditional design goals, such as relatively low power consumption, relatively high performance (e.g., speed), and relatively low circuit area, are also considerations that often need to be taken into account when designing VCO circuitry.
Deficiencies exist in existing VCO circuitry that can make them undesirable or unsuitable for certain transceiver applications. For instance, the “LC-tank” VCO architecture relies on an inductance and a capacitance to define a baseline oscillation frequency for the VCO's output clock signal. Although such an approach can yield relatively low phase noise, the frequency range is also relatively narrow. In addition, the LC-tank VCO architecture often consumes relatively large circuit area and a relatively large amount of power.
In view of the foregoing, it would be desirable to provide methods and apparatus that can generate a clock signal with relatively high bandwidth and relatively low phase noise. In addition, it would be desirable to provide such methods and apparatus with relatively low power consumption, relatively high performance, and relatively low circuit area.